In the above change speed transmission system, the stepless transmission is shiftable to stage-divide a combined driving force of engine output and the output of the stepless transmission or a combined driving force of engine output and the output of an electric motor into a plurality of speed ranges, and to output a driving force resulting from each speed range subjected to stepless speed changing. When this is used in driving a travel device, change speed transmission is realized advantageously, such as smoothing traveling speed changes, and simplifying shifting operations.
As this type of change speed transmission system, what is described in Patent Document 1 has been developed previously. While embodiments in Patent Document 1 are described hereinafter in order to facilitate understanding of the present invention, this is not necessarily an acknowledgement that Patent Document 1 constitutes prior art providing a basis for determining novelty or obviousness of the present invention.
In Patent Document 1, three types of speed change transmission system are described. One of the three speed change transmission systems (what is illustrated in FIG. 2 of Patent Document 1) includes a stepless transmission, a planetary transmission device, a clutch device, a third planetary transmission mechanism, and a brake for acting on the third planetary transmission mechanism.
The stepless transmission has a hydraulic pump of the variable displacement type with a pump shaft interlocked to an engine output shaft through a main clutch, and a hydraulic motor driven by pressure oil from this hydraulic pump.
The planetary transmission device has a first planetary transmission mechanism and a second planetary transmission mechanism. Planet gears of the first planetary transmission mechanism and planet gears of the second planetary transmission mechanism are interlocked by engagement between interlocking gear portions provided on the respective planet gears. The planet gears of the first planetary transmission mechanism and the planet gears of the second planetary transmission mechanism are supported by a carrier common to the first planetary transmission mechanism and second planetary transmission mechanism.
The clutch device has a first clutch, a second clutch, a third clutch and a fourth clutch. The first clutch has an input side rotary member interlocked to a ring gear of the second planetary transmission mechanism through an interlocking mechanism. The second clutch has an input side rotary member interlocked to a sun gear of the second planetary transmission mechanism through a rotary shaft. The third clutch has an input side rotary member interlocked to a carrier of the planetary transmission device through an interlocking mechanism.
The interlocking mechanism interlocking the input side rotary member of the first clutch and the ring gear of the second planetary transmission mechanism has a clutch side transmission gear meshed with the input side rotary member of the first clutch, a planetary side transmission gear meshed with the ring gear of the second planetary transmission mechanism, and a rotary shaft connected to the clutch side transmission gear and planetary side transmission gear. The interlocking mechanism interlocking the input side rotary member of the third clutch and the carrier of the planetary transmission device has a clutch side transmission gear meshed with the input side rotary member of the third clutch, a planetary side transmission gear meshed with the carrier, and a rotary shaft connected to the clutch side transmission gear and planetary side transmission gear.
The sun gear of the third planetary transmission mechanism is interlocked to an output side rotary member of the first clutch and second clutch, and the input side rotary member of the third clutch. The carrier of the third planetary transmission mechanism is interlocked to an output side rotary member of the third clutch and fourth clutch.
The brake is switchable between an engaged state for exerting braking action on the ring gear of the third planetary transmission mechanism, and a disengaged state for canceling the braking action on the ring gear.
With the speed change transmission system illustrated in FIG. 2 of Cited Document 1, output of the stepless transmission and the driving force of the pump shaft of the stepless transmission (engine drive not undergoing change speed action by the stepless transmission) are combined by the planetary transmission device. By shifting the stepless transmission, and by properly switching the first to fourth clutches and the brake between engaged state and disengaged state in timed relationship with the shifting operation, the combined driving force outputted from the planetary transmission device is stage-divided into a first speed range to a fourth speed range, and each speed range is put through stepless speed changing to be outputted from a carrier shaft of the third planetary transmission mechanism.
Another one (what is illustrated in FIG. 12 of Patent Document 1) and the other (what is illustrated in FIG. 16 of Patent Document 1) of the three speed change transmission systems described in Patent Document 1 have a stepless transmission, a planetary transmission device, a clutch device and an auxiliary change speed device.
The stepless transmission and planetary transmission device have the same constructions as the stepless transmission and planetary transmission device of the speed change transmission system illustrated in FIG. 2 of Patent Document 1.
The clutch device has a first clutch and a second clutch. The first clutch has an input side rotary member interlocked to the ring gear of the second planetary transmission mechanism of the planetary transmission device through an interlocking mechanism. The interlocking mechanism has a planetary side transmission gear meshed with the ring gear of the second planetary transmission mechanism, a clutch side transmission gear meshed with a gear portion of the input side rotary member of the first clutch, and a rotary interlocking shaft connected to the planetary side transmission gear and clutch side transmission gear.
The auxiliary change speed device has a high-speed clutch and a low-speed clutch. In the auxiliary change speed device illustrated in FIG. 16 of Patent Document 1, the high-speed clutch and low-speed clutch are dog clutches.
With the speed change transmission systems illustrated in FIG. 12 and FIG. 16 of Cited Document 1, output of the stepless transmission and the driving force of the pump shaft of the stepless transmission (engine drive not undergoing change speed action by the stepless transmission) are combined by the planetary transmission device. By shifting the stepless transmission, and by properly switching the first clutch, second clutch, high-speed clutch and low-speed clutch between engaged state and disengaged state in timed relationship with the shifting operation, the combined driving force outputted from the planetary transmission device is stage-divided into a first speed range to a fourth speed range, and each speed range is put through stepless speed changing to be outputted from an output shaft of the auxiliary change speed device.
In the case of a speed change transmission system employing the above conventional technique, the first to fourth clutches, or the first and second clutches and the high-speed and low-speed clutches, provided for stage-dividing the combined driving force from the planetary transmission device into a plurality of speed ranges for transmission to the output rotary member are arranged in the fore and aft direction of a transmission case, and tend to be large in the fore and aft direction of the transmission case.
Another problem of the conventional speed change transmission system is power cutting accompanying a shifting operation. A conventional speed change structure that can inhibit the power cutting accompanying a shifting operation is described in Patent Document 2.
The speed change transmission system described in Patent Document 2 has a first transmission line and a second transmission line arranged in parallel between a transmission shaft located upstream with respect to transmission for receiving engine power (hereinafter called the upstream transmission shaft) and a transmission shaft located downstream with respect to transmission for transmitting power to a travel device (hereinafter called the upstream transmission shaft). A transmission clutch of the hydraulic multi-plate type is disposed downstream of the first and second transmission lines. Between the upstream transmission shaft and first transmission line is a first gear speed change mechanism having a plurality of speed positions, and the first transmission line includes a first friction clutch. Between the upstream transmission shaft and second transmission line is a second gear speed change mechanism having a plurality of speed positions, and the second transmission line includes a second friction clutch. Between the first transmission line and downstream transmission shaft is a first auxiliary gear speed change mechanism having a plurality of speed positions. Between the second transmission line and downstream transmission shaft is a second auxiliary gear speed change mechanism having a plurality of speed positions.
The first gear speed change mechanism has a shift member operable by a first actuator, and the second gear speed change mechanism has a shift member operable by a second actuator. The first auxiliary gear speed change mechanism has a shift member operable by a first auxiliary actuator, and the second gear speed change mechanism has a shift member operable by a second auxiliary actuator.
The first actuator, first auxiliary actuator, second actuator and second auxiliary actuator are linked to a control device. The control device, based on a result of detection of a control position of the shift lever and a speed change mode selected by a setting switch, operates the first actuator to shift the first gear speed change mechanism, operates the second actuator to shift the second gear speed change mechanism, operates the first auxiliary actuator to shift the first auxiliary gear speed change mechanism, and operates the second auxiliary actuator to shift the second auxiliary gear speed change mechanism.
In a state where the shift lever is operated to one of a first speed position to an eighth speed position, the first gear speed change mechanism, first auxiliary gear speed change mechanism, second gear speed change mechanism and second auxiliary gear speed change mechanism are operated to a speed change state corresponding to the operated position of the shift lever. The power of the upstream transmission shaft is transmitted to the downstream transmission shaft through one of the first and second transmission lines.
When, for example, a second speed change mode is selected and the shift lever is operated from the first speed position to the fifth speed position, in the first half of speed change control accompanying this shifting operation, a double transmission state occurs in which power is transmitted to the downstream transmission shaft in a state where the shift member of the first gear speed change mechanism is in a first speed position, and simultaneously therewith and in addition thereto power is transmitted to the downstream transmission shaft in a state where the shift member of the second gear speed change mechanism is in a second speed position. In the second half of the speed change control, a double transmission state occurs in which power is transmitted to the downstream transmission shaft in a state where the shift member of the second gear speed change mechanism is in a second speed position, and simultaneously therewith and in addition thereto power is transmitted to the downstream transmission shaft in a state where the shift member of the first gear speed change mechanism is in a third speed position.
Even if torque variations arise in the double transmission states, the torque variations are absorbed by the transmission clutch in a half-transmission state slipping to some extent.
When speed changing is realized while inhibiting the power cutting by employing the above conventional technique, torque variations in the double transmission states are absorbed by slips of the friction clutches and transmission clutch. Then, when the double transmission states occur, it has been necessary to weaken operating forces that pressurize the friction clutches and transmission clutch to the half-transmission state, so that slips of the friction clutches and transmission clutch occur conveniently, thereby reliably avoiding damage to the transmission case and others. That is, a transmission loss in the double transmission states has tended to become large.
Patent Document 1:    Unexamined Patent Publication No. 2007-92949
Patent Document 2:    Unexamined Patent Publication No. 2003-343712